Originally posted by: kranky
It's a battle of wills. Discover is betting one of three things will happen.
1. You forget to make the two purchases a month at some point, giving them the right to cancel your 0% BT.
2. You pay late, same outcome.
3. You start liking Discover so much, you make bunches of purchases so they start collecting interest from you.
On the other hand, you are betting you will make exactly two very, very small purchases each and every month until the 0% BT is paid off.
Remember that your payment is first applied to the lowest-rate balance, so all your two-a-month purchases will be racking up interest until your 0% BT is fully paid.
You want to read the fine print to see under what conditions you forfeit your 0% BT. If it says that they can change your promotional rate at their discretion if they see anything on your credit report they don't like, then there is risk. But that risk isn't all that great, because if for some reason they try to yank it out from under you, you can always refi into a used car or personal loan using the car as collateral.
There is some risk, no absolute guarantee.